The Early Moderns defined substance in a variety of ways: that thing which holds all properties of an object together, the thing that remains once all properties are removed, or "the I know not what". Some, like Berkeley and Hume, denied the existence of substances all together.

The Nature of Substance



Locke

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(29 August 1632 – 28 October 1704)

Locke's beginning definition of substance is that which we know must exist but cannot give specific qualities to. Because ideas are not self producing or sufficient, we must acknowledge a "substratum" that can support them. We can only understand this substratum as standing under or upholding everything.
"...not imagining how these simple ideas can subsist by themselves, we accustom ourselves to suppose some substratum in which they do subsist and from which they do result, which therefore we call substance." (Locke, An Essay Concerning Human Understanding, Ch XXIII)

Substance - Aquiring the Idea
(how to understand substance according to Locke)
a. Reflection
b. Constancy
c. Individuality
d. Understanding
e. Cohesiveness
f. Demonstration





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Turtles all the way down: ancient Hindu cosmology includes the myth that the world rests on the back of a giant elephant which in turn stands on a giant turtle. As you move down the chain, however, each animal must be supported by something else, causing an infinite regress.
Locke employs this imagery to illustrate how our ideas must always adhere in something, the most basic tier being the "I know not what", that Locke defines as substance.



Arguments against Substance



Berkeley

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(12 March, 1685 – 14 January, 1753)
As shown in the first dialogue between Hylas and Philonous, Berkeley believes that for a thing to exist, it has to exist in the mind by being perceived. Furthermore, reality is only "real" insofar as it is perceived. If a tree were to fall in the forest, and there were no there to perceive it, not only would it not make a sound, it would not exist. However, Berkeley would say that it would occur because God is present. As a thinking spirit, God would know and therefore, the tree would exist, and when it fell, it would make a sound.

Much like Descartes, Berkeley believed that he could tell he existed by simply thinking he existed. He thought that he was a spirit. Berkeley believes that there is no external world, but that God is the substratum which holds everything together. God presents our finite spirits with whatever reality he chooses.

Hume

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(7 May 1711 – 25 August 1776)

"An object may exist and yet be nowhere, and I assert not only that it is possible but that the greatest part of beings do and must exist after this manner." (Treatise, I.4.5)

After saying this relatively shocking statement, Hume explains that he isn't talking about things that have extension. The only things that exist that are somewhere are things that are perceived by sight and touch. A moral reflection cannot be somewhere because you cannot put it to the right of, left of or under something. That, according to Hume, would be ridiculous.

"(N)o external object can make itself known to the mind immediately and without the interposition of an image or perception."

Hume argues that we do not really know objects, but rather know them through perceiving them.

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